Means for starting compressors in unloaded state



Dec. 21, 1965 K. w. B. LUNDVIK 3,224,663

MEANS FOR STARTING COMPRESSORS IN UNLOADED STATE Filed May 13, 1963 FIG. 7.

Karl 144E. Lu/mlw'k United States Patent Ofiflce 3,224,653 Patented Dec. 21, 1965 3,224,663 MEANS FOR STARTING COMPRESSORS IN UNLUADEED STATE Karl Wilhelm Bertil Lundvilt, Norriroping, Sweden, as-

signor to Sta Refrigeration Airtiebolag, Norrkoping,

Sweden, a corporation of Sweden Filed May 13, 1963, Ser. No. 279,775 2 Ciaims. (Cl. 230-29) The present invention relates to compressors and more particularly to means to improve the starting and the capacity regulation of compressors of the type having one or more cylinders and pistons reciprocating therein.

Hereinafter the invention will be described, by way of example, as applied to a compressor for use in connection with a refrigerating system, it being noted, however, that the invention is by no means restricted to compressors for such use.

It is already known to reduce the capacity of the compressor of a refrigerating system by permitting gas to flow back to the suction side from the compressor cylinder. By this expedient it is possible in a simple way to provide a capacity regulation without appreciably impairing the indicated efiiciency at partial load. The gas thus flowing back to the suction side of the compressor has only been subjected to a compression work of no importance, the essential compression work being effected after the piston has passed the overflow passage on its upward stroke.

By positioning the overflow passage at an appropriate distance from the top of the piston it is possible to obtain the exact maximum reduction desired. For various reasons a complete reduction of the capacity is not desired. In the event of too great a reduction the speed of the gas flow in the suction channel will be decreased to such an extent that the gas flow is not able to return any oil from the evaporator of the refrigerating system to the complessor. As a rule, a minimum capacity of 25% to 50% is usually aimed at. A capacity between full effect and minimum effect may be obtained by varying the cross sectional area of the overflow passage, for

instance, by means of a usual regulator valve. Maximum effect is obtained with said valve closed and minimum effect with the valve opened.

It is also already known to render the capacity regulation above referred to automatic, for instance, by means of a slide valve moving in a cylindrical bore under the control of a hydraulic pressure or the like for covering the overflow passage. By having this slide valve to more or less cover the overflow passage a continuous variation from maximum to minimum capacity may be eflected. A drawback inherent to such a capacity regulation system is that the compressor is not in unloaded state during the starting period. The most unfavourable position at starting is when the piston or any of the pistons, as the case may be, has just covered the overflow passage. As a result, the gas enclosed in the compressor cylinder will be subjected to compressing action from the very beginning of the starting period and discharged through the self-operating pressure valve. As a rule, one of the pistons of a multi-cylinder compressor will stop by itself in said unfavourable position when the electric current is cut off and the compressor is allowed to run til it stands still by itself. This is the reason why an electric motor having a great starting torque must be used in connection with compressors having the above described type of capacity regulation.

The present invention relates to compressors having one or more cylinders with pistons reciprocating therein and has for its object to provide means for securing both a starting of the compressor in unloaded state by the provision of one or more closeable passages between the innermost portion (top portion) of the cylinder and the suction chamber, said passages being such a small cross sectional area that the volume of the waste space will not be appreciably influenced, and a capacity regulation by means of one or more other adjustable passages extending between a point of the cylinder located at a given distance from the top thereof and the suction chamber.

A feature of the invention involves that the cross sectional area of the passages for unloaded starting and the passages for capacity regulation are controlled by one and the same regulating slide valve. In the event of a compressor driven by an electric motor, which is usually the case, the requirement of a high starting torque of said motor may be reduced, allowing the use of a Y-A-starting which has proved advantageous from economical point of view.

The invention is illustrated in the accompanying drawing, in which FIG. 1 is a part sectional side elevation of the top portion of a two-cylinder compressor and FIG. 2 is a part sectional plan, the section being taken along the line IIII of FIG. 1.

The gas to be compressed is admitted to the suction chamber 1 of the compressor which is in communication with a similar suction chamber provided in the top cover 2. From the last-mentioned chamber the suction gas is passed through suction valves, not shown, mounted in an intermediate plate 3 and enters the cylinders 4 of the compressor in which the pistons 5 reciprocate. The compressed gas is discharged through pressure valves, not shown, which are also mounted in plate member 3.

Formed in the cylinder wall are overflow passages 6 for connecting the compressor cylinders 4 with a pair of regulating cylinders 7 which in their turn communicate with the suction chamber 1. Reciprocating in each regulating cylinder is a regulating slide valve 8 covering to a more or less great extent the openings of overflow passages 6. The uppermost portion of each compressor cylinder is also in communication with the regulating cylinders 7 through drilled holes 9. Said holes open at such points of the regulating cylinders as to be uncovered by the slide valve 8 only after the latter has uncovere-d the normal overflow passages 6.

The slide valve 8 is acted on by forces in two directions. Acting in one direction is a spring 10 tending to move the slide valve in a direction to uncover the overflow passages 6; in the opposite direction the slide valve is acted on by a variable oil pressure tending to cause the slide valve to cover said overflow passages. By varying the last-mentioned pressure according to the need of refrigerating effect a corresponding variation of the capacity of the compressor may be obtained.

The said oil pressure acting on the slide valve is obtained from a pump 11 delivering a constant oil pressure to its discharge conduit. Said conduit is formed with a throttled portion 12 acting as a capillary pipe. Beyond said throttled portion the conduit is branched off to the oil inlets 13 of the regulating cylinders 7. Through bores 14 drilled in the walls of the regulating cylinders 7 at a distance from the tops of the regulating cylinders 7 the oil is discharged to a regulating valve 15 and thence to the suction chambers of the compressor.

When the piston-like bottoms of the slide valves 8 are on a level with the outlets 14 the overflow passages 6 should be completely open, while the additional overflow holes 9 should be still covered. The last-mentioned holes are to be uncovered only when the slide valve reaches its extreme position.

Provided in the regulating valve 15 is a diaphragm 16 rigidly connected to a conical valve body 17 which cooperates with a seat 18. Acting on the upper surface of said diaphragm is an adjustable spring 19 and prevailing below the diaphragm is the suction pressure.

The area of flow through the regulating valve 15 depends on the pressure acting on the suction side of the compressor. If the suction pressure is too high, which indicates too small a capacity, the regulating valve is held closed. The pressure inside the regulating cylinders will then be equal to the pump pressure and is sufficient to overcome the action of spring 10, thereby causing the slide valve to cover the overflow passages 6 leading to the compressor cylinder with a resulting increase of capacity. Too low a suction pressure will in an analogous way give rise to the following cycle of operations:

The regulating valve is opened so as to allow oil to be discharged to the suction side. The flow of oil through the capillary pipe causes a fall in pressure with a resulting reduction of the pressure in the regulating cylinders. The slide valves 8 move outwardly uncovering a great deal of the overflow passage with a resulting capacity reduction.

Outgoing from the pump conduit at a point thereof on the side of the capillary pipe 12 remote from the pump is a branch of conduit leading to the suction side of the compressor. Inserted in said branch conduit is a magnetic valve 21 open when the compressor stands still with the electric motor connected in Y-position, that is to say, during the starting period. With the motor connected in A-position, that is to say under normal operation, said magnetic valve is closed.

As long as the compressor is operating and the oil pump is delivering oil under pressure, the extreme position of the slide valves 8 is on a level with the outlets 14. In this position of the slide valves the regulating valve is open and an oil flow is passing through the regulating device. Thus, the drilled overflow holes 9 will not be in action, not even at minimum capacity, and their influence on the capacity will consequently not be greater than that corresponding to the increase of waste space.

At standstill as Well as at starting with the magnetic valve 21 in open state, the slide valves 8 are moved by their springs 10 int otheir extreme positions, thereby opening the overflow holes 9 between the top portion of the compressor and the suction chamber. The gas enclosed during the starting period between the overflow passages 6 and the tops of the compressor pistons is allowed to flow back to the suction side of the compressor against no high resistance. The torque required to rotate the compressor shaft is decreased, thereby allowing the use of the cheap Y-A-starting.

Due to the low piston speed at the starting moment the holes 9 need only a small area of flow. Their part of the total waste space will thus be so small that the capacity at full eflect will only be but very slightly influenced by the inventive device.

If deemed advisable the regulating valve 15 may be replaced by other means, as for instance, a magnetic valve without causing any change of the function of the device.

I claim:

1. In combination in a compressor, means forming a suction chamber, means forming at least one cylinder having an extreme end portion, a reciprocable piston in said cylinder, means for allowing starting of the compressor in unloaded state, said means comprising an interruptable conduit of a small cross-sectional area of passage connected between said extreme end portion of said cylinder and said suction chamber; and means for effecting a capacity regulation including a conduit between a portion of said cylinder spaced a distance from said extreme end portion of said cylinder and the suction chamber, and a slide valve for controlling both of said conduits.

2. In a compressor as claimed in claim 1 the further feature that said slide valve is arranged to completely uncover both of said conduits during the starting period and at standstill and that during operation to variably uncover said latter conduit.

References Cited by the Examiner UNITED STATES PATENTS 877,492 1/1908 Doelling 23025 1,036,934 8/1912 Toaz 23025 1,154,798 9/1915 Palmer 23022 1,481,358 1/1924 Dwyer 23046 1,632,841 6/1927 Le Valley 23031 1,899,002 2/1933 Le Valley 23029 1,903,853 4/1933 Ruff 23022 2,036,898 4/ 1936 Twisleton-Wykeham-Fiennes et al. 23022 2,038,176 4/1936 Hull 23029 2,172,751 9/1939 Heinrich 23031 2,715,992 8/1955 Wilson 23031 2,761,616 9/1956 Newton 23031 3,076,593 2/1963 Newton 23022 3,114,498 12/ 1963 Glass 23031 3,119,550 1/1964 West et al 23022 LAURENCE V. EFNER, Primary Examiner.

ROBERT M. WALKER, Examiner. 

1. IN COMBINATION IN A COMPRESSOR, MEANS FORMING A SUCTION CHAMBER, MEANS FORMING AT LEAST ONE CYLINER HAVING AN EXTREME END PORTION, A RECIPROCABLE PISTON IN SAID CYLINDER, MEANS FOR ALLOWING STARTING OF THE COMPRESSOR IN UNLOADED STATE, SAID MEANS COMPRISING AN INTERRUPTABLE CONDUIT OF A SMALL CROSS-SECTIONAL AREA OF PASSAGE CONNECTED BETWEEN SAID EXTREME END PORTION OF SAID CYLINDER AND SAID SUCTION CHAMBER; AND MEANS FOR EFFECTING A CAPACITY REGULATION INCLUDING A CONDUIT BETWEEN A PORTION OF SAID CYLINDER SPACED AND DISTANCE FROM SAID EXTREME END PORTION OF SAID CYLINDER AND THE SUCTION CHAMBER, AND A SLIDE VALVE FOR CONTROLLING BOTH OF SAID CONDUITS. 